A. Field of Invention
This invention pertains to the art of methods and apparatuses regarding vehicle automatic transmission systems, and more particularly to methods and apparatuses regarding engine power reduction during automatic transmission up-shifting.
B. Description of the Related Art
Automatic transmissions include a plurality of gears and associated components that are manipulated to drive an output shaft using different gear ratios. A transmission controller monitors vehicle operating conditions and driver input to determine whether an up-shift or a down-shift should occur. As is well known in the art, during an up-shift an on-coming component gradually engages a next gear as an off-going component gradually disengages the present gear. Typically, the release of the off-going component is controlled based on the rate of the on-coming component during the up-shift. One example of a control system for an automatic transmission is provided in U.S. Pat. No. 5,746,680 titled CONTROL SYSTEM FOR AUTOMATIC TRANSMISSIONS, which is incorporated herein by reference.
Automatic transmission clutch-to-clutch up-shifting can be divided into two distinct phases: the torque phase and the inertia phase. The torque phase initiates when the on-coming clutch pressure becomes sufficiently high to begin transmitting torque. This is typically judged by a pressure switch in the fluid (typically hydraulic fluid) circuit used to adjust the clutch. The torque phase ends and the inertia phase begins when the gear ratio actually begins to change. This is typically judged when the gear ratio exceeds a threshold setting. The inertia phase is finished when the on-coming clutch is completely engaged (that is, no slip).
Shift-quality depends, in part, upon the accuracy in adjusting clutch pressures relative to the level of engine torque being transmitted. It is known that the level of engine torque transmitted may be estimated based on engine load and engine output shaft speed. As the automatic transmission shifts between gear ratios, one clutch gradually disengages (that is, is off-going) as another clutch gradually engages (that is, is on-coming). This process may be referred to as clutch-to-clutch up (or down) shifting. The decrease and increase of pressure of the off-going and on-coming hydraulic clutches, respectively, determines, at least in part, the operator's feel or ride comfort. It is also known in the automotive industry that during clutch-to-clutch up-shifting in an automatic transmission vehicle, it is beneficial for both passenger shift feeling and clutch durability to temporarily reduce engine power. Engine power reduction is typically achieved by retarding the ignition timing and/or closing the electronically controlled throttle.
One known method for clutch-to-clutch up-shifting reduces engine power in a manner calculated to achieve a substantially complete reduction of engine power at some predetermined point prior to the transition from the torque phase to the inertia phase. This method has the disadvantage of substantial shift-shock and ride discomfort. Another known method achieves substantially complete reduction of engine power during the inertia phase. This method has the disadvantage of increased wear of the automatic transmission components and reduced reliability of the automatic transmission.
What is needed is a method for clutch-to-clutch up-shifting that substantially eliminates both shift-shock and increased wear of the automatic transmission components while simultaneously providing for increased passenger ride comfort.